Generation of Microwave Elastic Vibrations in a Disk by Ferromagnetic Resonance

Abstract

A calculation is presented of the generation of microwave elastic waves by the uniform precession resonance in ferromagnets. The excitation of the thickness shear modes in a normally magnetized ferromagnetic disk is treated. For uniform precession the elastic modes are driven only on the surfaces of the disk. The effects of long wavelength spin waves magnetostrictively driven by the elastic waves can be included in the analysis by a change in the elastic modulus. The coupling out of the elastic energy by bonding the disk to a non‐magnetic delay medium is considered for arbitrary values of the elastic impedances of the two media. An equivalent electrical circuit for transducers is presented; the efficiency and bandwidth of disk transducers are calculated for a disk placed in a matched one port resonant cavity. A figure of merit for such transducers is defined, and calculated for yttrium iron garnet. Due to interference between the elastic waves generated on the two disk surfaces, the realizable bandwidth of the transducer is restricted by the thickness of the disk. By bonding two disks together or by using a rod, this restriction may be reduced.